Automatic tarpaulin assemblies are commonly used in the trucking industry to cover truck beds carrying items that might fall or be blown out of the truck bed were it not for the tarpaulin. Many of these automatic tarpaulin systems have a spring-biased roller onto which the tarpaulin is rolled. The inventor's prior U.S. Pat. No. 5,292,169, which is hereby incorporated by reference, discloses such an automatic tarpaulin system. FIGS. 1 and 2 also show such a tarpaulin assembly 2 mounted on a truck 1. For simplicity, the truck 1 in FIG. 1 is depicted without any side walls on the truck bed. In FIG. 2, all parts of the truck 1 other than the truck bed have been removed.
As shown in FIGS. 1 and 2, the tarpaulin assembly 2 has two jointed side arms 4 which can be extended and retracted by hydraulic cylinders provided on the assembly 2. Disposed between the side arms 4 towards their ends is a roller shaft 11 on which a tarpaulin roller 6 is rotatably mounted. The roller 6 is spring-biased on the roller shaft 11 in a counter-clockwise direction (from the vantage point of FIGS. 1 and 2). A tarpaulin 3 is secured to the roller 6 at one end and to the truck 1 at the other end. As best shown in FIG. 2, the end of the tarpaulin that is attached to the truck 1 is provided with a rigid member 14 running the width of the tarpaulin 3 which rests in and is secured to at least one tarpaulin cradle 13 mounted on the truck 1. In most systems, a cross member 5 is mounted between the side arms 4 adjacent and parallel to the roller shaft 11 to provide added stability to the assembly 2.
When it is desired to cover the bed of the truck 1 with the tarpaulin 3, the side arms 4 are extended away from the cab of the truck 1 to the position shown in FIG. 1. As the side arms 4 extend, the tarpaulin 3 is unrolled from the roller 6, overcoming the spring-biasing force of the roller 6. To uncover the truck bed, the side arms 4 are retracted to the position shown in FIG. 2. This allows the spring-biasing force of the roller 6 to roll the tarpaulin 3 back up onto the roller 6.
In some automatic tarpaulin systems, such as the one shown in FIG. 3, the roller 6 is mounted on a stationary support 16 near the cab of the truck 1 rather than at the end of the side arms 4. The end of the tarpaulin 3 that is not attached to the roller 6 is attached to the cross member 5. Such a system usually includes an air foil (not shown) covering the roller 6 to reduce wind resistance. Other than the placement of the roller 6, the layout and operation of the system shown in FIG. 3 is the same as that of FIGS. 1 and 2.
Although tarpaulins 3 are usually made of canvas or some other sturdy material, they may become sufficiently worn after extensive use so as to require replacement. Replacement of worn-out tarpaulins 3 in spring-biased tarpaulin assemblies 2 of the type shown in FIGS. 1, 2, and 3 has traditionally been a very laborious and time consuming endeavor. This is because the spring-bias of the roller 6 makes it impossible to replace the tarpaulin 3 while the roller 6 is still attached to the assembly 2. Therefore, prior art tarpaulin replacement methods have always required the removal of the roller 6 from the assembly 2.
The following is a summary of the tarpaulin replacement procedure for an automatic tarpaulin assembly 2 of the type shown in FIGS. 1 and 2. Although there are some minor variations, the procedure for the system shown in FIG. 3 is roughly analogous.
The procedure begins by fully retracting the side arms 4 to the point shown in FIG. 2. Next, the end of the tarpaulin 3 having the rigid member 14 is detached from the tarpaulin cradle 13. The roller 6 and roller shaft 11 are then detached from the side arms 4, thus freeing the tarpaulin 3 and roller 6 from the rest of the assembly 2 and relieving the tension biasing the roller 6. Once free, the roller 6 must be carried to a large open area and placed on the ground to provide room for the rest of the replacement procedure. This is no small task as the roller 6 with the tarpaulin 3 completely rolled up on it can be quite heavy. Once the roller 6 is on the ground, the tarpaulin 3 must be completely unrolled from the roller until the attachment of the tarpaulin 3 to the roller 6 is exposed. This attachment, usually several screws, is then removed to free the tarpaulin 3 from the roller 6. stop to the roller preferably comprises an outwardly-projecting stem for engaging a hole provided in the side of the roller when the roller-shaft-engaging portion engages the roller shaft.
If the tarpaulin assembly has a cross member disposed adjacent and parallel to the roller shaft, the handle portion of the stop may rest against the cross member to prevent rotation of the roller. If the tarpaulin assembly does not have a cross member, but has side arms between which the roller shaft is mounted, the handle portion of the stop may be provided with an outwardly-extending side member which can rest against one of the side arms to prevent rotation of the roller.
The tarpaulin replacement method comprises the steps of unrolling the tarpaulin from the roller against the spring-biasing force of the roller until the attachment of the tarpaulin to the roller is exposed, securing the roller against rotation, detaching the tarpaulin from the roller, attaching a new tarpaulin to the roller, releasing the roller, and allowing the spring-biasing force of the roller to cause the roller to rotate, thereby rolling the new tarpaulin onto the roller. Preferably, the steps of detaching the tarpaulin from the roller and attaching a new tarpaulin to the roller are performed while the roller and the roller shaft are still attached to the tarpaulin assembly.
The step of securing the roller against rotation preferably comprises securing a roller stop to the roller, and allowing the spring-biasing force of the roller to cause the roller and the roller stop to rotate back until the roller stop comes to rest against part of the tarpaulin assembly or part of the truck, thereby preventing further rotation of the roller. The step of releasing the roller preferably comprises removing the roller stop from the roller. The method preferably also comprises the step of providing a hole in the side of the roller, the hole being adapted to engage a stem provided on the roller stop to secure the roller stop to the roller.
Because the apparatus and method of the present invention prevent the roller of the tarpaulin assembly from rotating under the spring-biasing force during a tarpaulin replacement procedure, the tarpaulin may be replaced without having to remove the roller and the roller shaft from the assembly. This saves considerable time and effort over the prior art replacement method.
Next, a new tarpaulin 3 is laid out over the old tarpaulin. This new tarpaulin 3 is then attached to the roller 6 and rolled up on it. The roller 6 (including the roller shaft 11) and the new tarpaulin 3 must then be carried back to the truck 1 and lifted up onto the tarpaulin cradle 13. The end of the tarpaulin 3 having the rigid member 14 is attached to the tarpaulin cradle 13 and the roller 6 and roller shaft 11 are reattached to one of the side arms 4. Next, the roller 6 is tensioned so that it will once again be spring-biased in the counter-clockwise direction. Finally, the roller 6 is reattached to the other side arm 4. The entire replacement process often requires three to four man-hours to complete.
Clearly, the process would be greatly simplified if the tarpaulin 3 could be replaced without having to remove the roller 6 from the assembly 2. This would avoid: (i) the difficulty associated with detaching the roller 6 and roller shaft 11 from the side arms 4, (ii) the work involved with lowering the roller 6 and carrying it away from the truck 1, (iii) the heavy lifting involved with carrying the roller 6 back to the truck 1 and lifting it into place, (iv) the difficulty associated with reattaching the roller 6 and roller shaft 11 to the side arms 4, and (v) the need to re-tension the roller 6 after the tarpaulin 3 is replaced so that it is once again spring-biased.